The prior art is exemplified by U.S. Pat. No. 4,335,764 issued 22 June, 1982 for an invention of Charles J. Schmidt entitled "Veneer Peeling Apparatus". Schmidt provides a spindleless or centerless veneer peeling lathe having a fixed roller and two movable rollers. A block to be peeled is positioned between the rollers, which are rotatably driven against the block, thereby rotating the block. As the block rotates, the movable rollers are moved towards the fixed roller, thus forcing the block into a knife mounted near the fixed roller, which peels veneer from the rotating block.
In Schmidt's apparatus, the two movable rollers are positioned at equal distances from the fixed roller at all times. This is achieved with the aid of a timing means, such as a pair of gears, which mechanically couple the movable rollers to each other and prevent movement of one roller without equal movement of the other. Such mechanical coupling of the movable rollers constitutes a significant practical disadvantage, because it does not permit precise control of the geometric relationship between the block and the knife during peeling of the block, due to the inability to move one of the movable rollers without a corresponding equal movement of the other movable roller. Such precise control is often desired in particular cases to ensure production of high quality veneer of uniform thickness. The type and condition of the wood which is to be peeled may for example necessitate continuous variation of the geometric relationship between the block and the knife during peeling of the block in order to achieve optimal results.
A further disadvantage of Schmidt's apparatus is that the movable rollers are mounted on support beams which must be swung, relatively rapidly, through curved paths as the block is peeled. The support beams have a high rotational inertia. Thus, high power input is required to move the beams. Moreover, control problems are encountered, due to the susceptibility of the swinging beams to harmonic oscillations as they swing through their working arcs.
The present invention overcomes the disadvantages aforesaid by mounting the movable rollers such that at least one of them may be selectably positioned with respect to the other two rollers in response to a control signal generated by a computer, thereby facilitating control of the geometric relationship between the block and the knife.
A still further disadvantage of Schmidt's apparatus is that the two movable rollers rotate at the same speed (disregarding minor speed variations which are introduced as the gear drive is actuated to swing the rotatably driven rolls through their curved working paths). Although Schmidt provides for a difference of about one percent in the speed of the fixed roller, in comparison to the speed of the movable rollers, there is no provision for varying the rotational speed of each roller independently of the rotational speed of the other rollers. Roller speed variation is advantageous because it enables the rollers to accurately follow the surface of the rotating block, without skidding against the block surface and wasting power or interfering with the peeling operation. Because the block is peeled in a spiral, the rollers must each rotate at slightly different speeds which vary continuously as peeling proceeds. Variable control of the speed of each roller, which is a feature of the present invention, also facilitates ejection of the peeled block core from the lathe when the peeling operation is completed, and loading of a fresh block into the lathe.